1. Field of the Invention
This invention relates to heat developable imaging materials and processes for developing a dye-enhanced silver image employing in reactive association (a) photosensitive silver halide, (b) an image-forming combination comprising (i) a silver salt of a certain 1,2,4-mercaptotriazole derivative with (ii) a phenylenediamine or aminophenol silver halide developing agent, (c) a compound that contains a coupling moiety and which forms a dye upon reaction with the oxidized form of the developing agent, (d) a binder, and (e) an antifoggant concentration of a thiazoline thione antifoggant. In one of its aspects it relates to a photothermographic element comprising a support having thereon the described photosensitive silver halide and combination of imaging materials and an antifoggant concentration of the thiazoline thione antifoggant. In another of its aspects it relates to a photographic composition, especially a photothermographic composition, comprising the described photosensitive silver halide and imaging composition with the antifoggant concentration of the thiazoline thione antifoggant. A further aspect of the invention relates to a process of developing a dye-enhanced silver image in a photographic material, especially a photothermographic material, containing the described imaging combination and the thiazoline thione antifoggant.
2. Description of the State of the Art
It is known to provide an image in an imaging material, especially a photographic imaging material, by what is known as dry processing with heat. Such an imaging material is often described as a heat developable photographic material or photothermographic material. Such heat developable photographic materials after imagewise exposure are heated to moderately elevated temperatures to provide a developed image in the absence of a processing solution or bath. Typical heat developable imaging materials or photothermographic materials are described, for example, in U.S. Pat. No. 3,801,321 of Evans et al, issued Apr. 2, 1974; U.S. Pat. No. 3,152,904 or Sorensen et al, issued Oct. 13, 1964; U.S. Pat. No. 3,457,075 of Morgan et al, issued July 22, 1969; U.S. Pat. No. 3,392,020 of Yutzy et al, issued July 9, 1968; and British Specification No. 1,161,777 published Aug. 20, 1969.
The most commonly used silver salts in such heat developable photographic materials, especially photothermographic materials, are silver salts of long-chain fatty acids, such as silver behenate, which generally require hydrophobic binders. It has been desirable to replace these silver salts of long-chain fatty acids to enable use of aqueous or other hydrophilic compositions which further enable the use of conventional silver halide emulsion technology in heat developable photographic materials. Use of silver behenate as a source of silver in heat developable materials is not particularly compatible with aqueous formulations of photosensitive silver halide materials. Other silver salts or complexes have been proposed for such heat developable photographic materials. These include, for example, silver salts of benzotriazole, saccharin and related silver salts or complexes. These are described, for example, in heat developable photographic materials in U.S. Pat. No. 3,617,289 of Ohkubo et al, issued Oct. 2, 1971; U.S. Pat. No. 3,666,477 of Goffe, issued May 30, 1972; U.S. Pat. No. 3,672,904 of deMauriac, issued June 27, 1972; U.S. Pat. No. 3,832,186 of Masuda et al, issued Aug. 27, 1974; British Specification No. 1,205,500 published Sept. 16, 1970; U.S. Pat. No. 3,689,270 of Anderson et al, issued Sept. 5, 1972; and Research Disclosure, Volume 150, Item 15026, October 1976, pages 18-21, published by Industrial Opportunities Ltd., Homewell, Havant Hampshire, PO9 1EF, UK. While many of these silver complexes or salts can provide an image in such heat developable photographic materials, they often provide less than desired processing temperature latitude, photographic speed, image tone, or a combination of one or more of these problems. The photographic materials also in some cases have required the presence of what has been described as a "melt-forming compound" to provide a desired developed image.
It is desired in many cases to spectrally sensitize heat developable photographic materials to enable exposure to other than the blue region of the visible spectrum. Difficulty is often encountered in spectrally sensitizing photosensitive silver halide to be used in heat developable materials. While in many cases some degree of spectral sensitization can be provided, it is often insufficient for many photographic purposes. It has been desirable to provide a heat developable silver halide photographic material which enables a dye-enhanced silver image and which is based on photographic silver halide technology which permits use of a broader range of spectral sensitizing dyes.
Silver salts of a variety of heterocyclic compounds are known for various purposes in photographic materials. Examples of such uses of silver salts are described in U.S. Pat. No. 2,353,754 of Peterson, issued July 18, 1944 and U.S. Pat. No. 3,794,496 of Manhart, issued Feb. 26, 1974.
A common problem encountered in heat developable photographic materials centers on instability of the image following processing. Often heat developable photographic materials have required addition of a separate post-processing image stabilizer or stabilizer precursor to provide desired post-processing stability. Examples of stabilizer precursors in photothermographic materials are described, for instance, in U.S. Pat. No. 3,839,041 of Hiller, issued Oct. 1, 1974. Dye enhancement of silver images in photographic materials, however, provides additional problems. One of the problems is undesired fog upon processing which is not answered by a stabilizer precursor that does not adequately release a stabilizing moiety within the desired time. No suitable answer to this undesired fog is found in the described art.
A photothermographic material has been described comprising in reactive association (a) photosensitive silver halide, (b) an image-forming combination comprising (b) an image-forming combination comprising (i) a silver salt of certain 1,2,4-mercaptotriazole derivatives with (ii) a silver halide developing agent, and (c) a polymeric binder. This photothermographic material is described in Research Disclosure, June 1977, pages 80-81, Item 15869, of P. D. Knight, R. A. deMauriac and P. A. Graham. An image in this material can be developed after imagewise exposure by merely heating the material to moderately elevated temperatures. However, it has been desirable to provide an additional imaging means in this photothermographic material. The additional imaging material, however, can provide additional problems such as fogging problems in the imaging mechanism during development. No answer to this problem has been obtained from the art described.
It is also known to provide a dye image to enhance a silver image in a photographic material. This is described, for example, in U.S. Pat. No. 2,266,456 of Wilder, issued Dec. 16, 1941; British Specification No. 1,096,049 published Dec. 20, 1967; British Specification No. 614,808 accepted Dec. 23, 1948; U.S. Pat. No. 3,622,629 of Lugosy, issued Nov. 23, 1971; and British Specification No. 515,022 accepted Nov. 23, 1939. No answer to the problem of fog in a photographic material, especially a photothermographic material, comprising an image-forming combination of photosensitive silver halide with a silver salt of certain 1,2,4-mercaptotriazole derivatives and a phenylenediamine or aminophenol silver halide developing agent is found in this art.
There has been a need for improved photographic materials producing a dye-enhanced silver image having reduced fog when using a photosensitive silver halide with an image-forming combination comprising a silver salt of certain 1,2,4-mercaptotriazole derivatives. This need has been especially important for photothermographic materials comprising the described image-forming combination. There has also been a need for improved photothermographic materials comprising a described image-forming combination to provide a dye-enhanced silver image which enable improved post-processing image stability in the absence of a separate image stabilizer or stabilizer precursor.